This invention relates to a bicycle with an electric motor and more particularly to an electric motor assisted, pedal operated vehicle.
There have been proposed pedal operated vehicles such as bicycles wherein there is provided an electric motor which is designed so as to assist the operator in the pedal operation. These electric motor assists may be employed to provide added power when going up hills or for infirmed people. However, the construction is such that the amount of electric assist is proportional to the force which the operator puts on the pedal. In this way, it will be insured that safety can be maintained and that the operator will still obtain the benefit of physical exercise when operating the vehicle.
Normally, these type of devices incorporate some form of force sensing mechanism, generally on the output side of the pedal operator, at which the operator's pedaling force is being sensed. These force sensors thus do not actually sense directly the force which the operator exerts with his feet but rather the output force of the pedal mechanism. It should be noted that because of the crank angle of the pedal mechanism, a given operator force will provide a cyclically varying output force from the pedal mechanism. This force varies from a minimum force when the pedals are at top or bottom dead center and a maximum force when the pedals are at 90.degree. from top or bottom dead center positions.
Although these types of mechanism are quite useful and serve well their intended purposes, there are some areas which can be improved. For example, it is desirable to insure that the user cannot inadvertently bypass the force sensing mechanism so as to provide electric power which is not related to the pedal force mechanism. In addition, the pedal force sensing mechanism, being a mechanical device and being subject to the elements, can be subject to corrosion or other factors that can cause the force sensing mechanism to provide an incorrect or inaccurate force signal.
The ways in which these inaccurate signals can occur may be understood by reference to FIGS. 1 through 3 which are graphical views that show the force sensing signal from the pedal torque sensor in the curves F.sub.L1, F.sub.L2 and F.sub.L3, which show the actual pedaling force transmitted from the operator to the pedals and outputted from the crank mechanism by the broken line curve P and a predetermined minimum output force F.sub.L0. The dot dash (. -) curve F.sub.L0 normally represents the minimum force which must be exerted by the pedals before the electric motor assist occurs.
FIG. 1 shows a condition when the operator has intentionally bypassed the output of the force sensor so as to provide an output signal F.sub.L1 which is at a fixed value. If this is done, then the electric motor which assists the pedal mechanism will operate continuously at a relatively high output. This can present a number of disadvantages.
FIG. 2 is a view showing the condition that will happen if the torque sensor has friction which retards it from returning to its normal state once the maximum torque is sensed and the torque decreases. The output signal F.sub.L2 will be seen to fall off less gradually than the pedal force P and when the pedal force P again increases to the fallen level of the sensor F.sub.L2, then the torque sensor will again track actual torque until the peak is again passed. As a result, unnecessarily high electric motor assist will occur.
FIG. 3 shows another type of malfunction which can occur if an obstruction occurs somehow in the torque sensor so that the torque sensor can only fall to a predetermined low torque indicated by the horizontal line of the torque curve F.sub.L3. Above this point, the actual torque will be sensed but no lower torque signals will sensed. Again, this will provide an inaccurate reading and excessive electric motor assist.
It is, therefore, a principal object to this invention to provide an improved type of electric motor assist for a pedal operated vehicle wherein the system will assure against incorrect electric motor assist.
It is a further object to this invention to provide an electric motor assisted power pedal operated vehicle wherein the operator cannot intentionally bypass the output of the torque sensor.
It is a further object to this invention to provide an electric motor assisted pedal operated vehicle mechanism wherein the system will not provide excess electric power assist in the event of some malfunction in the output of the torque sensor.
In connection with such electrically assist pedal operated vehicles, it has already been noted that the electric motor assist is related to the actual pedaling force. However, when starting up, the operator may exert a very high force on the pedals and if this force is transmitted into a proportionate electric motor assist, too much assist may be provided.
It is, therefore, a still further object to this invention to provide an electric motor assisted pedal operated vehicle wherein the electric assist on start up is retarded so as to insure against abrupt increase in electric motor assist during start up.